souring a dark mild, does it need more gravity?

I brewed 10 Gallons of an English dark mild, split into two 5 gallon carboys, one got 1968 English ale, the other was a repitched roeselares cake, about 6 months old. The sour dark mild went from 1.041 to 1.009 in about 7 days. It has a nice Brett character and a very mild tartness and a bit thin, though to be expected for such a young and lower gravity brew.

I'm wondering if I should add some gravity, like malto dextrin and pour in some dregs or is 9 points enough to ride out another 6 to 9 months?

I may be wrong, but you will just get a stronger beer at the end, as the brett will just eat the maltodextrine.

I ended up adding about 8oz of malto-dextrin. After a few months, this did exactly what I needed. It upped the mouthfeel just enough to not be considered thin. So far it's picking up some nice sour notes.